The transistor amplifier with high input impedance, low output impedance, and current gain of less than one is the common?

The common collector transistor amplifier, often referred to as an emitter follower, is characterized by having high input impedance and low output impedance, making it ideal for impedance matching applications. The key feature that defines this configuration is that the output is taken from the emitter, which follows the input signal at the base while providing current gain of less than one. This means that while the voltage may be buffered, the configuration does not amplify power in the sense of increasing current, but rather it serves to interface components that operate at different impedance levels.

The high input impedance is advantageous for minimizing the load on the previous stage of the circuit, and the low output impedance helps drive the next stage effectively. This configuration is often used in scenarios where voltage buffering is needed without adding significant gain, making it suitable for applications like signal coupling and isolation.

The other configurations—such as common base and common emitter—serve different purposes. The common emitter typically provides higher voltage gain, while the common base configuration offers low input impedance, which is not suitable in this context.